In 9ac1ab10c963a86457c2c9b1edf31542ff3737cd this library function was
refactored to use mkfs.ext4 instead of cptofs. There are two problems:
If populateImageCommands would create no files (which is fine), a cp
invocation would fail due to missing source arguments.
Another problem is that mkfs.ext4 relies on fakeroot to have sane
uid/gids in the generated filesystem image. This currently doesn't
work for cross compiling.
fd2047c642